Many golfers have one or two favorite clubs, which they refer over the rest of the clubs in their set. The favorite club(s) usually feels and performs better for the golfer. If the golfer could duplicate the performance of this favorite club and make each of the clubs in his set feel and perform like his favorite club, the golfer could improve his game.
That a golfer finds a difference in behavior of one club from another in a set is not surprising due predominantly to normal shaft manufacturing tolerances. Shafts made from the same die can vary substantially. For example, steel shafts of a leading manufacturer are permitted to vary by up to .+-.2.5% in stiffness and still be within tolerance. With the difference between "regular" and "stiff" shafts or "stiff" and "extra stiff" being only about 2.5%, a shaft within a set can vary all the way from "regular" to "extra stiff" even though all the shafts in the set were made from a "stiff" die.
Attempts at duplication of a golf club to copy a single golf club or to produce a matched set of clubs are well known in the art. A variety of different methods have been proposed to accomplish these difficult tasks. One of the most popular techniques involves the determination of and then matching the natural frequency of the clubs or, in some instances, the club shafts. U.S. Pat. Nos. 3,395,571; 4,070,022; 4,122,593; 4,555,112; and 4,736,093 and U.K. Application No. 2,223,951 each disclose methods of duplicating golf clubs and/or producing matched golf club sets by means of club or shaft natural frequency matching.
U.S. Pat. No. 3,698,239 discloses a method of producing a dynamically matched set of clubs by starting with a favorite club, determining its moment of inertia of mass for a selected swinging axis by calculation from its length and weight, and producing the remaining set to have the same moment of inertia, by calculation. The use of the moment of inertia in the duplication of golf clubs is also disclosed in U.S. Pat. No. 4,128,242.
U.S. Pat. No. 4,175,440 discloses dynamic testing and matching of clubs by measuring the angular velocity and centrifugal force along the axis of the club shaft as the club is swung on an arcuate path using an adjustable power rotational drive means.
Overall mass matching is used in U.S. Pat. No. 4,415,156 to produce a matched set of clubs.
In U.S. Pat. No. 4,900,025 a correlated set of clubs is made by matching the shaft flexure characteristics such that the deflection of a reference point is substantially uniform when a given torque is applied at the point.
None of these techniques, however, have developed enough or in some cases the right information about a particular club to enable one to accurately and completely duplicate the club so that the duplicate club performs and feels like the club being duplicated.
Also, none of these techniques have developed enough or in some cases the right information about a particular club to enable one to accurately and completely match other clubs in a set so that matched club(s) perform and feel like the first club.
Particularly, the prior art has not recognized that club or shaft selectivity (or damping factor or bandwidth) are important to the proper selection of a club for a particular player. The art has not related a golf club's ability to perform to its capacity to forgive off-speed swings.
Moreover, the art has not adequately addressed the issue of how to select a "pattern" club so as to produce a set of clubs appropriate for a particular individual. It has been left up to a player or his teacher or clubfitter to attempt to select an initial club for replication throughout a set of golf clubs.
Accordingly, it is an object of the present invention to develop a method and device to either duplicate a golf club or to produce a matched set of clubs so that the golfer using the produced clubs can not tell the difference between the clubs.
It is a further object to differentiate golf clubs based upon their selectivity for forgiving off-speed swings.
It is a still further object to scientifically determine which golf club of a series has the appropriate selectivity for a particular golfer.
It is another object of this invention to alter a golf club's selectivity by selection of shaft material and shaft construction methods and to alter Q of existing clubs by changing clubhead weight and grip hardness.
It is an object of this invention to measure a golfer's swing speeds with a multiplicity of test clubs and to perform statistical calculations and a device for measuring, storing, calculating and displaying swing speed characteristics such as mean speed for swings taken with each test club and the statistical variation, sigma, of a normal distribution of the same swings. The optimum test club frequency is revealed by these statistics: the best club is associated with the highest average swing speed of each sample and the lowest sigma.